The disclosed invention relates to a paper feed mechanism or the like for use in high speed printers or typewriters and specifically to pressure rollers for pressing a paper sheet or web against a platen permitting the web to be advanced as the platen is rotated.
In the field of paper printers, typewriters and the other similar machines, a paper feed mechanism is provided to advance a paper sheet or web so as to present fresh paper to a printing mechanism. Once the fresh paper has been printed on, the sheet or web is advanced again to permit further printing on fresh paper during subsequent printing operations.
The paper feed mechanism of a printer or typewriter frequently is in the form of a pressure roller for pressing the sheet or web against a platen which is rotated after each line is printed to advance the sheet or web to present fresh paper to the printing mechanism. The pressure roller typically takes the form of a rubber coated cylindrical body mounted for rotation on an axle. The cylinder is spring biased toward the platen and disposed for rotation about an axis parallel to the axis of rotation of a platen. A paper sheet or web is fed between the roller and the platen and the spring bias on the roller is sufficient to maintain intimate contact between the platen and the paper sheet or web. As the platen is rotated, the sheet or web is advanced.
In some arrangements, each pressure roller has a plurality of freely rotatable cylindrical portions disposed in spaced relation to each other along each axle, with each cylindrical portion being made with a rubber coating suitable for driving contact with a paper sheet or web. Often a plurality of such pressure rollers are spring biased toward the platen of a printing mechanism to conform a paper sheet or web to the surface of the platen and permit the paper sheet or web to advance past a printing position as the platen is rotated.
As is well known to those skilled in the art, such prior art pressure rollers are quite adequate for use in typewriters and printers where the paper feed rate is relatively slow. In such applications, the operator must take care to align the paper carefully as the feed mechanism will feed the paper at the same angle to the platen thereafter. If the paper sheet or web is not correctly aligned, it will gradually shift relative to the platen so the print margin will shift relative to the edge of the sheet or web. But aside from the initial alignment problem which is problematical with most paper feed systems of the type described, such paper feed mechanisms usually cause the sheet or web to become somewhat misaligned as the paper is fed through the printer. This problem is especially acute when long fan fold webs are used as the misalignment introduced by the paper feed mechanism is cumulative as paper is fed through the printer.
In attempting to overcome this problem, alternative feed systems have been used in high speed printers. The most frequently used feed is one using a sprocket wheel for engaging sprocket holes along the longitudinal edges of the paper being printed on. After printing, the sprocket holes along the paper edges can be removed, if desired, on some fan fold paper webs by separating the edges with the sprocket holes therethrough along slit perforations in the web which run parallel to the edge. The sprocket feed for such printers, however, contribute to manufacturing expense due to the cost of sprocketed drive mechanisms and to paper cost due to the requirement of edge perforation. A further problem arises from the fact that the printer must be adjusted when paper of different width is used. The mechanism permitting such adjustment to accomodate different paper width is expensive.
In view of the problems associated with known paper feed mechanisms, it is the primary objective of the present invention to provide a paper feed mechanism suitable for use in a high speed printer which does not cause a paper sheet or web fed therethrough to become misaligned.
It is a further objective of the invention to provide a paper feed mechanism for highspeed printers and the like which is not complex in structure yet is suitable for use with many different paper widths without requiring adjustment.
It is yet another objective of the invention to provide a paper feed mechanism which is operable at high speed in either direction and does not cause paper skew or bunching.
It is still another objective of the invention to provide a paper feed mechanism operable at high speed in either direction and is easily manufactured and does not require careful adjustment.